1. Field of the Invention
The invention relates to a pressure sensor having pressure transmission capability and a method for manufacturing such sensors.
2. Description of the Related Art
British Patent No. 1,065,192 discloses a pressure sensor comprising a pot-type metal housing in which a first chamber is formed by a diaphragm assembly comprising a solid disk of relatively small diameter surrounded by a thin metal diaphragm, the diaphragm assembly limiting the first chamber in which a pressure transducer is placed surrounded by liquid filled in the first chamber. A second diaphragm assembly is fixedly attached to an annular ring that in turn is fixedly attached to the housing by screws. Resilient 0-rings seal mating surfaces between the ring and the housing. The second diaphragm assembly comprises a solid disk of a diameter much larger than that of the disk of the first diaphragm assembly and is surrounded by a thin metal diaphragm member. A distance stud connects the large disk with the small disk for direct force transmission. This known pressure sensor is of complex design and difficult and expensive to be manufactured.
JP 61-88120 A in Patents Abstracts of Japan P-495, Sep. 9, 1986 Vol. 10/No. 264 discloses a pressure transducer comprising an annular supporting body having a thin diaphragm rigidly fixed to one end surface. A pressure transmitting rod is fitted to the opposite side of the pressure receiving surface. The diaphragm, the supporting body, and the transmission rod are made of ceramics and are joined and adhered with powder glass. One end of a cantilever including a strain gauge is adhered to the supporting body with glass and the free end is contacted with the rod without being fixed. The cantilever constitutes a strain gauge by selectively diffusing impurity into a single crystal silicone substrate. By such a design the strain gauge is protected against contamination due to a medium the pressure of which is to be detected. No pressure transmission capability is disclosed.
French Patent No. 1,447,317 discloses a pressure sensor comprising a metal block provided with an inlet for pressurized fluid, an outer peripheral surface of said block being provided with a threading for having screwed thereon an annular ring spanned by a first diaphragm of large diameter. A second metal ring is in turn screwed to the first metal ring and is spanned by a second diaphragm provided with a resistor bridge. A force transmission stud extends between the two diaphragms for direct force transmission therebetween. The threaded connections are subject to leakage; furthermore, it is extremely difficult to exactly adjust the distance between the two diaphragms and bridge said force transmission rod. A similar sensor has been disclosed in European Patent Application No. 0 145 146.
U.S. Pat. No. 4,864,271 discloses pressure sensors made of ceramic material by successively placing a plurality of ceramic layers on top of each other followed by sintering this combination to an integral body, one of the layers forming a diaphragm.
U.S. Pat. No. 3,611,797 discloses a strain gauge transducer comprising an annular housing spanned by a strip supporting a strain gauge assembly.